Enthesitis Common in Psoriatic Arthritis

Enthesitis, the inflammation of the entheses -- where tendons or ligaments insert into bone -- affects about 35% of patients with psoriatic arthritis (PsA), with the most common sites the Achilles tendons, plantar fascia, and lateral epicondyles, new research shows.

The study -- the first to look at enthesitis among PsA patients -- also found that risk factors for developing enthesitis include more actively inflamed joints, higher body mass index (BMI), and, interestingly, younger age.

The study results, published in Arthritis Care & Research, suggest that enthesitis is "an important feature" of PsA and should be assessed regularly in these patients, said the senior author, Dafna Gladman, MD, of the University of Toronto. "Hopefully, doctors will assess patients with PsA for the presence of enthesitis, and especially the areas that we have identified occurring most commonly."

The study included 803 patients from the PsA Clinic at the University of Toronto. The mean age of the study group was 50.8, the mean PsA duration was 12.3 years, and the mean psoriasis duration was 22.2 years.

Of the 803 subjects, 281 had enthesitis on at least one visit -- for a prevalence of 35%.

This prevalence, said Gladman, was not surprising, and might be expected to be even higher, given that enthesitis is a "well-known feature of psoriatic arthritis."

Enthesitis was defined for the study as the presence of at least one tender site of the 18 in the SpondyloArthritis Research Consortium Canada (SPARCC) enthesitis index, which has been recognized as valid and reliable for patients with PsA.

Patients without enthesitis served as controls in the study.

Among the patients with enthesitis, the mean age at enthesitis detection was 49, and the duration of having PsA was 11.4 years. At the time of enthesitis, the mean BMI was 30, and 47% of patients were obese (BMI over 30). The mean number of actively inflamed joints was 9.5, and the mean damage joint count was 3.8.

Almost a third of these patients (31%) had an elevated erythrocyte sedimentation rate (ESR), 41% had elevated C-reactive protein (CRP), and 14% were positive for human leukocyte antigen-B27 (HLA-B27). Radiological evaluation showed plantar spurs in 53% of these patients, Achilles spurs in 37%, and sacroiliitis in 42%.

The three most common tender entheseal sites were Achilles tendon insertion in 24.2% of patients, plantar fascia in 20.8%, and lateral epicondyles in 17.2%.

The authors noted that the lower body sites were more commonly involved: "The reason behind this might be the higher load that causes more repetitive biomechanical stress at the enthesis, leading to an inflammatory reaction in the joint and the attachment sites, which may be more pronounced in the lower extremities," the authors noted.

About 15% of the group with enthesitis were also diagnosed with fibromyalgia. However, the most commonly detected sites were clearly distinguished clinically from the fibromyalgia tender points, and the analysis did not reveal a significant association between enthesitis and fibromyalgia.

It's not surprising "at all" that patients with enthesitis have more severe disease, Gladman said, adding that it is also not unexpected that heavier patients are more likely to have enthesitis since high BMI predisposes to the development of bony spurs, which may be associated with enthesitis.

What was surprising, however, was the association with younger age.

"We might have expected enthesitis to increase with age, but our study actually showed that young people are more likely to have it. This fact might support the concept that the enthesitis is not age-related but is indeed related to the underlying disease."

The median time to enthesitis resolution was 7.5 months. The majority of patients were treated with medications, but most improved without changing treatment, and the analyses failed to identify any treatment that was associated with or predicted enthesitis. However, the authors pointed out that the study was not designed to address treatment efficacy for enthesitis.

A limitation of the study was the inclusion of patients who had a relatively long disease duration, the authors said. Earlier disease may present differently, possibly with more active sites.

Commenting on the study for MedPage Today, Scott Zashin, MD, a rheumatologist in private practice in Dallas, said that for him, the study results suggest that "enthesopathy is underappreciated" in PsA.

The condition, possibly present in up to about a third of patients, can have a significant effect on activities of daily living, Zashin said. "In addition to examining joints during follow up visits, it's important to also check common sites for enthesitis, including, but not limited to, the Achilles tendon, plantar fascia, and lateral epicondyle."

The authors reported that they do not have any potential conflicts of interest related to the study.